Operation and control of a multi-terminal DC network

The development of multi-terminal dc (MTdc) networks will be of extreme importance to allow further penetration of power electronic converters to serve dc loads in low (LVdc), medium (MVdc) and high-voltage (HVdc) applications. One attracting application for MTdc networks, especially in Northern Europe, is the integration of offshore wind farms using voltage-source converters (VSC). The present work wishes to analyze the operation and control of a MTdc network. First, the dynamic models of the VSC, the MTdc network and dc cables are presented. The VSC is described by a linear small-signal model and its controllers are optimized via a multi-objective genetic algorithm. Subsequently, the VSC models are validated using two 5-kVA VSC connected in back-to-back through LVdc cables. To validate the models, the test results are compared with simulation results. Next, two strategies for controlling MTdc networks are presented and compared: a droop control and a novel strategy called distributed voltage control. Finally, conclusions about the operation and control of MTdc networks are drawn on basis of the performed experiments and simulations.